Figure 18.8
GEO-GRAPHIC: How sand migrates. (A) All active sand dunes have a relatively gentle slope on the windward side (facing into the prevailing wind) and a steeper slope on the leeward side, called the slip face. This sand dune is in the southern Namib Desert in coastal Namibia. (B) A cross section of a sand dune reveals the cross-bedding structure created on its leeward side. (C) Cross-bedding can be seen in the Navajo sandstone formation in Zion National Park, Utah. These fossilized dunes are nearly 200 million years old.(A. © ALESSANDRO DELLA BELLA/Keystone/Corbis; C. Peter Carlson/Flickr RF/Getty Images)